<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>按钮1</button>
    <button>按钮2</button>
    <button>按钮3</button>
    <button>按钮4</button>
    <button>按钮5</button>
    <script>
        // 1.获取所有按钮元素
        var btns = document.getElementsByTagName('button');
        for(var i =0 ;i< btns.length;i++) {
            btns[i].onclick = function() {
                // 先把所有的背景颜色改为无色
                for(var a =0 ;a< btns.length;a++) {
                        btns[a].style.backgroundColor='';
                }
                // 再把当前按钮的颜色改变
                this.style.backgroundColor='pink';
            }
        }
    </script>
</body>
</html>